1. Field of the Invention
The present invention particularly relates to a liquid discharge head having a vibrating plate member, and to an image forming apparatus.
2. Description of the Related Art
As an image forming apparatus such as a printer; a facsimile; a copying apparatus; a plotter; and a multifunction peripheral of these apparatuses, a liquid discharge recording type image forming apparatus using a recording head formed of, for example, a liquid discharge head (liquid droplet discharge head) that discharges ink droplets has been known. This liquid discharge recording type image forming apparatus performs image formation (recording, typing, imaging, and printing are used as synonyms) by discharging ink droplets from a recording head to a conveyed sheet (sheet is not limited to paper, but includes OHP (overhead projector) and the like, to which ink droplets, other liquid, and the like can attach. The sheet is also referred to as a medium to be recorded on, a recording medium, recording paper, a recording sheet, and the like). This liquid discharge recording type image forming apparatus includes a serial type image forming apparatus which forms images by discharging liquid droplets while moving a recording head in a main scanning direction, and a line type image forming apparatus using a line type head that forms images by discharging liquid droplets without moving a recording head.
In the present application, the liquid discharge recording type “image forming apparatus” means an apparatus that performs image formation by discharging liquid onto a medium such as paper, a string, a fiber, a cloth, a leather, metal, plastic, glass, wood, and ceramics. The “image formation” does not mean only to attach an image with a meaning such as text and a figure to a medium, but also to attach an image having no meaning such as a pattern to a medium (to simply land liquid droplets onto a medium). “Ink” is not limited to what is called an ink, but is used as a collective term for all liquid that can be used for image formation, such as what is called a recording solution, a fixation processing liquid, and a liquid. For example, a DNA sample, resist, a pattern material, resin, and the like are included in the “ink”. Further, the “image” is not limited to be two-dimensional, but also includes an image attached to a three-dimensionally formed object or an image formed by three-dimensionally shaping a solid itself.
As a conventional liquid discharge head, what is called a piezoelectric head has been known. The piezoelectric head includes a piezoelectric body serving as a pressure generating unit for pressurizing ink as liquid in a liquid chamber, such as a piezoelectric actuator using a stacked-layer type piezoelectric element having piezoelectric layers and internal electrodes that are alternately stacked. The piezoelectric head deforms a deformable vibration area of a vibration plate member that forms a wall surface of the liquid chamber by a displacement in a d33 or d31 direction of the stacked-layer type piezoelectric element, so as to change volume and pressure in the liquid chamber to discharge liquid droplets.
Such a liquid discharge head using the stacked-layer type piezoelectric element has the following characteristics. Since the vibration plate member can be driven at high frequency, individual liquid droplets can be landed as an aggregate. Since the size of the droplets to be discharged can be controlled from small droplets to large droplets, high quality printing can be performed at high speed.
In order to realize an image forming apparatus aiming for higher quality printing at higher speed, there has been a demand to arrange nozzles for discharging liquid droplets at a high density. However, in realizing a high density of the head using the stacked-layer type piezoelectric elements, so-called mutual interference is a problem. The mutual interference occurs such that, when a vibration area (diaphragm part) of a vibration plate member is displaced for discharging droplets, pressure fluctuation propagates to an adjacent liquid chamber, whereby droplets are discharged by the adjacent chamber unstably, or liquid dripping occurs from a nozzle when the adjacent chamber does not discharge droplets.
In view of these problems, a structure has been conventionally known (Patent Document 1) in which a pillar type piezoelectric element (drive pillar) for applying a driving signal to a piezoelectric member and a pillar type piezoelectric element (non-drive pillar) that does not apply a driving signal but serves as a support member are alternately arranged so that non-drive pillar supports a partition wall between liquid chambers. In this case, the drive pillar and non-drive pillar are used separately as follows by forming grooves in a stacked-layer type piezoelectric member. The drive pillar is formed to pressurize a liquid chamber for discharging droplets. The non-drive pillar is arranged at a position opposing a partition wall of a channel plate constituting the liquid chamber.
Further, to prevent the non-drive pillar from being extended by a force applied by the drive pillar when the drive pillar is driven, there have been known, for example, the following techniques to increase rigidity of the non-drive pillar. The non-drive pillar is formed of a material with an elastic coefficient greater than that of the drive pillar, a cross-sectional area of the non-drive pillar is formed greater than that of the drive pillar, or the cross-sectional area of the non-drive pillar is formed to be larger at the side farther from a vibration plate (Patent Document 2).
In addition, it has also been known to connect one of inactive areas positioned at opposite ends of a stacked-layer type piezoelectric element in a longitudinal direction of a pressure liquid chamber, via a vibration plate, to a pressure liquid chamber substrate (Patent Document 3).
[Patent Document 1]    Japanese Patent Application Publication No. 2002-292864
[Patent Document 2]    Japanese Patent Application Publication No. 2000-351207
[Patent Document 3]    Japanese Patent Application Publication No. 2004-160941
In a high density head having nozzles aligned at a high density, a pitch of grooves formed in a stacked-layer type piezoelectric element (piezoelectric member) becomes narrow. In addition, widths of the drive pillar and non-drive pillar (width in a direction in which the nozzles are aligned (hereinafter also referred to as “nozzle alignment direction”), the same applies below) also become narrow.
In this case, since the volumes of individual liquid chambers that are in communication with the nozzles become small, droplets have to be discharged at high efficiency. To discharge the droplets at high efficiency, a displacement amount of a diaphragm part of a vibration plate member has to be increased in order to generate high pressure in the liquid chamber by a low voltage drive. To increase the displacement amount of the diaphragm part of the vibration plate member, at least one of the following has to be increased: a displacement amount of a stacked-layer type piezoelectric element, namely, the number of active stacked layers; or an area which applies pressure to a vibration plate.
However, in forming the grooves in a stacked-layer type piezoelectric element, a depth of the groove to be processed is limited. Therefore, it is difficult to increase the number of stacked active layers.
On the other hand, it has become clear that the mutual interference is caused when the non-drive pillar undergoes an extensional deformation since the non-drive pillar is narrow and the rigidity of the non-drive pillar is decreased with respect to a deformation force caused by a diaphragm part of a vibration plate member deformed by a displacement of the drive pillar; thus the non-drive pillar cannot avoid the deformation. To suppress this extensional deformation of the non-drive pillar, it has been known to apply a staged-groove process, by which staged grooves are formed, in order to increase a cross-sectional area of the non-drive pillar, namely the width of the non-drive pillar as disclosed in Patent Document 2. However, if such a staged-groove process is applied, there is a problem in that a high density cannot be substantially realized.
Regarding a countermeasure for the mutual interference, it has been clarified that the technique disclosed in Patent Document 3 cannot prevent deformation of the non-drive pillar at a high density.